Biomedical optics is an emerging field with enormous potential to diagnose and treat diseases safely and economically. Success in application of biomedical optics is highly dependent on accurate characterization of optical properties of target tissues. Particularly, the interaction of a particular type of tissue with light needs thorough and accurate characterization to predict the interaction of light with such a tissue during treatment.
Integrating spheres provide a wealth of benefits, such as isotropic detection of reflectance from samples that reflect light and the ability to accurately measure even the lowest light intensities that are otherwise impossible to measure with other optical measuring techniques. The inherent symmetry of the integrating sphere provides an accurate means of measuring light intensity by diffusely distributing all light intensity evenly within its inner cavity. However, this advantage also comes with the disadvantage of destroying all spatial information from a sample. As such, there is currently no way of determining spatial data within an integrating sphere.
Further, the integrating sphere currently available suffers from a few limitations. The current industry-standard method for determining the optical properties of tissue involves taking both a transmittance and reflectance measurement to determine the absorption and scattering of light in the tissue. An extremely thin slice of tissue, typically thin enough to allow enough transmission of light through the thin slice, is necessary for such transmittance measurements. Preparation of such thin slices of tissue can be effected by using of a microtome device that appropriately slices a frozen tissue. However, the process of microtome takes time and expense. In addition, freezing of a sample tissue sample to enable microtome slicing introduces physically changes to the structure of the sample itself. As a consequence, the measured optical properties of a sample prepared by microtome can deviate from the true optical properties of an undamaged sample by the artifacts of the structural damage introduced into the prepared sample due to the freezing and the mechanical slicing.
In addition, the prior art method for determining optical properties within an integrating sphere requires manually moving the sample to different port positions in order to obtain both reflectance and transmission measurements. Since it is extremely difficult for the user to manually position the sample perfectly by visual inspection alone, the data collected represents an inconsistent measurement of the sample. A double-integrating sphere approach has been proposed in an attempt to solve this problem, in which the sample is placed in the rear of the first sphere which becomes the front of a second adjacent integrating sphere. Besides the high cost of having to purchase a second integrating sphere, this prior art technique is limited to extremely thin tissue samples, since light must be transmitted into the second integrating sphere for measurement.
Due to the lack of an accurate and economic method for determining optical properties within a standard integrating sphere optical measurement device, translation of optical biomedical devices and technologies from research laboratories to clinics have been hampered. Thus, there exists a need for standardized optical property measurement that provides accurate characterization of a sample without having to perform microtome slicing.